GB1584020A

GB1584020A - Gear pump

Info

Publication number: GB1584020A
Application number: GB11591/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-04-01
Filing date: 1978-03-23
Publication date: 1981-02-04
Also published as: AT353103B; IT1093500B; BE864919A; DE2714705B2; IT7821526A0; SE7802848L; AU523008B2; CA1103989A; AU3485278A; NL7803492A; FR2385918B1; FR2385918A1; ATA194978A; CH623116A5; DE2714705C3; DE2714705A1

Abstract

The pump contains a driving (1) and a driven (2) gearwheel, and also a multi-part casing with wear plates laterally enclosing the gearwheels. Disposed on the driving and/or driven tooth flanks of the gearwheels (1, 2) or on the inside of at least one of the wear plates of the casing in the region of the line of action (7) of the gearing there is at least one groove-like recess having a variable cross-section. (5). <IMAGE>

Description

(54) A GEAR PUMP (71) I, PAUL TRUNINGER, of Bahnweg 6, CH-4512 Bellach, Switzerland, of Swiss nationality, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed; to be particularly described in and by the following statement:- This invention relates to a gear pump comprising two intermeshing gears, of which one is a driving gear and is intended to rotate in one direction only and the other is a driven gear, accommodated in a housing including a pair of side plates in sealing engagement with the side faces of said gears. Such gear pumps are widely known and used.

Due to the geometrical shape of the teeth, the flow conveyed by these gear pumps is pulsating. In the literature and coefficient of fluctuation ô which is the characteristic factor for the flow stream pulsation is defined as Qmax Qmln AQ a= = Qmean Qo This flow stream pulsation is the cause of a pressure pulsation which appears for instance in pressure reduction through a throttle. One serious disadvantage of this pressure pulsation is the noise which is produced not only in the pump and throttle but in the entire hydraulic circuit. Further disadvantages are vibrations, caused by pressure pulsation, in plant components, oscillations in oil columns, and the load alternations on seals.

The coefficient of fluctuation of gear pumps cannot be reduced without limits.

By selection of suitable tooth parameters the coefficient of fluctuation can be reduced to below 2%, especially for internal gear pumps. However close limits are set to any further reduction, since economic aspects such as the specific output must also be considered.

While the geometrically-dependent flow stream pulsations in gear pumps are independent of outlet pressure, the pressure pulsations produced through a throttle due to flow stream pulsations (in a system free of natural oscillations) are proportional to the static pressure. The formula Pew=2 POA is applicable, e.g. with a static pressure P0 of 100 bar and b=2 /", the pressure pulsation amplitude Pw is 4 bar.

This in itself results in a considerable noise level.

However the internal leakage oil flows in pumps with constant clearances are proportional to the outlet pressure. Leakage oil flow pulsations therefore produce pressure pulsations through a throttle which increase as the square of the static pressure.

If now there is introduced a leakage oil pulsation which at a selected pressure PN (e.g. nominal pressure) has the same amplitude as the geometric flow stream pulsation, is in counter-phase therewith, and has the same variation curve, the resulting flow stream pulsation at the pump outlet for a static pressure PN becomes zero, and likewise the pressure pulsation disappears. When the pressure PN is exceeded the flow stream pulsation and with it the pressure pulsation increase again. A significant reduction in the pressure pulsations, though to varying extents, must therefore be expected over the whole range of pressures.

The object of the invention is to provide a gear pump of the type initially described wherein a reduction is obtained in the pressure pulsations caused by the flow stream pulsations, and also in the noise level.

According to one aspect of the present invention we provide a gear pump comprising two intermeshing gears, of which one is a driving gear and is intended to rotate in one direction only and the other is a driven gear, accommodated in a housing including a pair of side plates in sealing engagement with the side faces of said gears, characterised in that to compensate for the flow stream pulsation attributable to gear tooth geometry a leakage path is provided between the suction and pressure sides of the intermeshing teeth, said leakage path being constituted either by at least one recess formation of varying cross-sectional area in the torque transmitting flank of each tooth of at least one of said gears or in the sealing face of at least one of said side plates in the region of the line of contact of the intermeshing teeth, said recess formation or formations being so configured that the leakage flow variation created substantially matches and thereby counteracts said flow stream pulsation.

According to a second aspect of the present invention we provide a gear pump comprising two intermeshing gears, of which one is a driving gear and is intended to rotate in one direction only and the other is a driven gear, accommodated in a housing including a pair of side plates in sealing engagement with the side faces of said gears, characterised in that to compensate for the flow stream pulsation attributable to gear tooth geometry a leakage path is provided between the section and pressure sides of the intermeshing teeth, said leakage path being constituted by at least one recess formation of varying cross-sectional area in the torque transmitting flank of each tooth of at least one of said gears.

The geometrical flow stream pulsation varies sinusoidally in accordance with the following formula applicable to involute teeth:

where 1 is the angle of rotation. The flow stream reaches its maximum at the peak where the angle of rotation o,=O, i.e. the flank engagement point is on the line joining the centres of rotation of both gears. The minimum value is at the beginning or end of the engagement of a pair of teeth flanks. The compensating leakage oil flow therefore reaches its maximum value at the peak (P1= ) and is zero at the beginning and end of tooth engagement. (To simplify presentation, a zero overlap is assumed).

According to a preferred embodiment of the invention, the recess formations may comprise grooves extending along the flank fall lines of the associated teeth. In a further embodiment the recess formations can be provided at one or both sides as chamfers on the torque-transmitting tooth flanks of at least one of the gears.

The invention is described in more detail below for embodiments shown in relation to the drawings. In these:- Figure 1 shows the teeth in a first embodiment; Figure 2 is a detail from Figure 1, in perspective view; Figure 3 is the inside of the middle portion of the housing side plate in a further embodiment.

As seen from Figure 1, the gear pump in accordance with the invention consists of a driving gear 1, a driven gear 2, and a housing (not shown) which encloses both gears. The driving gear 1 which during operation rotates in the direction of arrow A, has in the fall line (i.e. the line of greatest slope) of the front flank 4 of tooth 3, a recess formation in the form of a groove 5 whose cross-section is greatest at the peak, while it reduces towards both sides and is bounded by the beginning or end of the engagement of a pair of teeth flanks.

Instead of providing a groove at the flank of only one gear tooth, as shown, the engaging teeth flanks of both gears 1, 2 may also be provided with such grooves.

According to a further embodiment, not shown, the recess formations may be in the form of chamfers located laterally on the torque-transmitting teeth flanks, being at the ends of the said flanks adjacent one or both sides of one or both gears.

Through suitable dimensioning of the varying cross-sections of the grooves it is possible for the leakage oil flow to be largely matched in amplitude and curve shape to the flow stream pulsation. It is limited by the cross-section at the particular sealing point, i.e. the point of contact which separates the suction and pressure sides.

With the further embodiment shown in Figure 3, a recess formation in the form of a groove 8 is provided in one of the two side plates 6 along the contact line 7 of the teeth. In this case again, the cross-section of the groove can be varied within wide limits by suitable dimensioning, and matched to the flow stream pulsations. Here too the sealing point, i.e. the point of contact which separates the suction side 9 from the pressure side 10, is by-passed by a leakage oil groove with a cross-section of varying size.

It will be understood that as a consequence of the pulsating leakage oil flow additional to the normal leakage oil flow, the volumetric efficiency drops. To avoid appreciable reduction in this efficiency, the features concerned can therefore only be utilised for those teeth which have a low coefficient of fluctuation. This applies especially to optimised internal teeth. In this case the efficiency drops by less than 1%, i.e. by a minor amount making hardly any difference in practice.

WHAT I CLAIM IS: 1. A gear pump comprising two intermeshing gears, of which one is a driving gear and is intended to rotate in one direction only and the other is a driven gear, accommodated in a housing including a pair of side plates in sealing engagement with the side faces of said gears, characterised in that to compensate for the flow stream pulsation attributable to gear tooth geometry a leakage path is provided between the suction and pressure sides of the intermeshing teeth, said leakage path being constituted either by at least one recess formation of varying cross-sectional area in the torque transmitting flank of each tooth of at least one of said gears or in the sealing face of at least one of said side plates in the region of the line of contact of the intermeshing teeth, said recess formation or formations being so configured that the leakage flow variation created substantially matches and thereby counteracts said flow stream pulsation.

2. A gear pump comprising two intermeshing gears, of which one is a driving gear and is intended to rotate in one direction only and the other is a driven gear, accommodated in a housing including a pair of side plates in sealing engagement with the side faces of said gears, characterised in that to compensate for the flow stream pulsation attributable to gear tooth geometry a leakage path is provided between the section and pressure sides of the intermeshing teeth, said leakage path being constituted by at least one recess formation of varying cross-sectional area in the torque transmitting flank of each tooth of at least one of said gears.

3. A pump as claimed in Claim 1 or 2 in which said gear teeth are of involute form and the leakage flow variation is sinusoidal.

4. A pump as claimed in any one of Claims 1 to 3 in which each flank recess formation comprises a groove extending along the flank fall line of the associated tooth.

5. A pump as claimed in any one of Claims 1 to 3 in which said flank recess formations comprise chamfers at the ends of said flanks adjacent to one or both sides of one or both gears.

6. A pump as claimed in Claim 1 in which the or each side plate recess formation is elongate in the direction of the line of contact of the intermeshing teeth.

7. A pump as claimed in Claim 6 in which the cross-sectional area of said recess formation diminishes towards each end thereof.

8. A pump as claimed in any one of Claims 1 to 7 in which the pump is of the internal gear type.

9. A pump as claimed in any one of Claims 1 to 7 in which the pump is of the external gear type.

10. A gear pump substantially as hereinbefore described with reference to, and as shown in, Figures 1 and 2 or Figure 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. With the further embodiment shown in Figure 3, a recess formation in the form of a groove 8 is provided in one of the two side plates 6 along the contact line 7 of the teeth. In this case again, the cross-section of the groove can be varied within wide limits by suitable dimensioning, and matched to the flow stream pulsations. Here too the sealing point, i.e. the point of contact which separates the suction side 9 from the pressure side 10, is by-passed by a leakage oil groove with a cross-section of varying size. It will be understood that as a consequence of the pulsating leakage oil flow additional to the normal leakage oil flow, the volumetric efficiency drops. To avoid appreciable reduction in this efficiency, the features concerned can therefore only be utilised for those teeth which have a low coefficient of fluctuation. This applies especially to optimised internal teeth. In this case the efficiency drops by less than 1%, i.e. by a minor amount making hardly any difference in practice. WHAT I CLAIM IS:

1. A gear pump comprising two intermeshing gears, of which one is a driving gear and is intended to rotate in one direction only and the other is a driven gear, accommodated in a housing including a pair of side plates in sealing engagement with the side faces of said gears, characterised in that to compensate for the flow stream pulsation attributable to gear tooth geometry a leakage path is provided between the suction and pressure sides of the intermeshing teeth, said leakage path being constituted either by at least one recess formation of varying cross-sectional area in the torque transmitting flank of each tooth of at least one of said gears or in the sealing face of at least one of said side plates in the region of the line of contact of the intermeshing teeth, said recess formation or formations being so configured that the leakage flow variation created substantially matches and thereby counteracts said flow stream pulsation.